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# Varying parameters in a simulation

Nothing should remain constant in a dynamic model. In this respect, Dinamica EGO enables to vary model parameters either in different simulation phases or at each time step. In the Stack tab, a set of Select Functors can be used to change the values of input parameters according to the model step.

**Using different transition matrices**

For examples, instead of using only a constant transition matrix, *Select Transition Matrix* enables the use of different transition matrices in a simulation.

To start, load the model `simulate_deforestation_using_multiple_transition_matrix.egoml`

from `\ advanced\multiple_parameters\simulate_deforestation_using_multiple_transition_matrix`

Using more than one transition matrix in a model is quite simple. In this version of a deforestation model, *Select Transition Matrix* was added to allow the choice of a transition matrix according to the model step. Each transition matrix is entered in a *Number Transition Matrix*, click on this functor with the Edit Functor.

**Matrix Number** in this functor indentifies the model step in which this transition matrix begins to operate. The model will use this matrix until it finds a *Number Transition Matrix* with **Matrix Number** that corresponds to the current model step, while from this point onwards *Select Transition Matrix* switches to the new transition matrix.

**TIP**: you can use as many transition matrices as time steps. You just need to add more

*Number Transition Matrix*functors and number them according to the model time intervals.

**Using different Weights of Evidence coefficients**

The same procedure applies to the selection of other model parameters, such as the Weight of Evidence
coefficients.
Load the model: `simulate_deforestation_using_multiple_transition_matrix_and_weights.egoml`

from `\Examples\advanced\multiple_parameters\simulate_deforestation_using_multiple_transition_matrix_and_weights`

A *Select Weights* functor is added to the model to enable the selection of more than one Weights of Evidence coefficient files. A *Number Weight* is inserted within the container *Select Weights* for each Weights of Evidence coefficient file. Another *Load Weights* is added to the model in the outside part of the main loop (*Repeat*). This functor loads the coefficients from a file and is connected to one of the *Number Weights* inside the *Select Weights*. Open each one of the *Number Weights* and edit the **Weight Number** field to define the step when each coefficient file begins to take part in the model.